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package byteDance;
import java.util.Stack;
/**
* Created by lizeyang on 2020/5/16.
* 链表正向相加，反向相加（在不改变链表结构的基础上）
*/
public class test43 {
//正向相加，时间复杂度O(max(m,n))
public static ListNode test(ListNode head1, ListNode head2) {
if (head1 == null) {
return head2;
} else if (head2 == null) {
return head1;
}
//carry表示进位
int carry = 0, sum = 0;
ListNode head = new ListNode(0), dummy = head;
head.next = null;
//注意采用尾插法
while (head1 != null || head2 != null || carry > 0) {
int value1 = head1 == null ? 0 : head1.val;
int value2 = head2 == null ? 0 : head2.val;
sum = value1 + value2 + carry;
carry = sum / 10;
ListNode node = new ListNode(sum % 10);
head.next = node;
head = node;
if (head1 != null) {
head1 = head1.next;
}
if (head2 != null) {
head2 = head2.next;
}
}
return dummy.next;
}
//反向相加，利用两个stack
public static ListNode backSum(ListNode head1, ListNode head2) {
if (head1 == null) {
return head2;
} else if (head2 == null) {
return head1;
}
Stack<ListNode> stack1 = new Stack<>();
Stack<ListNode> stack2 = new Stack<>();
while (head1 != null) {
stack1.push(head1);
head1 = head1.next;
}
while (head2 != null) {
stack2.push(head2);
head2 = head2.next;
}
int carry = 0, sum = 0;
ListNode head = new ListNode(0);
head.next = null;
//注意采用头插法
while (!stack1.isEmpty() || !stack2.isEmpty() || carry > 0) {
int value1 = stack1.isEmpty() ? 0 : stack1.pop().val;
int value2 = stack2.isEmpty() ? 0 : stack2.pop().val;
sum = value1 + value2 + carry;
carry = sum / 10;
ListNode node = new ListNode(sum % 10);
node.next = head.next;
head.next = node;
}
return head.next;
}
public static void main(String[] args) {
ListNode head1 = new ListNode(6);
head1.next = new ListNode(1);
head1.next.next = new ListNode(7);
ListNode head2 = new ListNode(2);
head2.next = new ListNode(9);
head2.next.next = new ListNode(5);
//正向相加
// ListNode res = test(head1, head2);
//反向相加
ListNode res = backSum(head1, head2);
while (res != null) {
System.out.print(res.val + " ");
res = res.next;
}
}
}